I don't understand why running a 1 bar cap would be a risk at normal coolant levels (asides for possible cavitation or boiling at localized hot spots... Which is a risk at any level). When the coolant expands, the air would just vent once the pressure started to go beyond 2 bar

While not being 100% sure, maybe a system constantly venting is not a healthy one. Think about the venting system being stuck open or in the worse but less likely case, stuck closed.

Quote:

Originally Posted by dknightd

Why do you assume a maximum operating temperature of 96 degrees Celsius?
That would be the ideal. Thermostat should be fully open by then. 96 in the block, less than that (on average) in the radiator. But if you are beating on the car in a hot climate it is very possible that the thermostat is always open, then the average temperature could exceed 96. If the average temp was 96 deg C then you would not need a pressurized system at sea level. I assume BMW designed a system that would work on any road, at any elevation, and any likely ambient temperature. But that type of system may not be ideal for some of us.

96 degrees is not the temperature in the block, it is what the coolant temperature sensor in the lower radiator hose measures. I used this value as an approximation of the coolant temperature inside the ET, which will maximize the pressure. We were trying to put a ceiling on the highest pressure, so as to err on the cautious side.

Temperature is probably much higher in the block, but of course not higher than the boiling point. Oil temperature might give a better estimation of that. INPA does have the capability of reading the oil temp.